1. Field of the Invention
This invention relates to an optical-fiber feedthrough that can make hermetic sealing for guiding an optical fiber into an optical communication module such as a semiconductor laser module or a semiconductor amplifier module, used in optical communication or the like. More particularly, it relates to an improvement of an optical-fiber feedthrough that can make an optical-fiber bare fiber not easily break when it is attached to a package sidewall of the optical communication module.
2. Description of the Related Art
In optical communication modules such as semiconductor laser modules, and semiconductor amplifier modules, a semiconductor element and an optical fiber are optically coupled inside the package. If the package is not hermetically sealed, any moisture having entered it from the outside may condense in the package to cause difficulties such that the optical element deteriorates and electrodes electrically short. Accordingly, what becomes important is the structure of hermetic sealing between the package and the optical fiber.
Hitherto, methods have been proposed in a large number and have been put into practical use. What is most common is a method in which a pipelike metallic sleeve is interposed between the package and the optical fiber to seal the package hermetically.
For example, Japanese Patent Application Laid-open No. H8-15572 discloses an optical-fiber feedthrough having a structure having i) an optical fiber constituted of a resin-covered portion at which the surface of an optical-fiber bare fiber is covered and an optical-fiber bare fiber uncovered portion standing uncovered from this resin-covered portion and ii) a pipe (metallic sleeve) with which this optical fiber is fastened, where the pipe and the optical-fiber bare fiber uncovered portion are soldered at the gap between them, and the gap between the pipe and the resin-covered portion are filled with an adhesive to bond them. Japanese Patent Application Laid-open No. H8-114723 also discloses an optical-fiber feedthrough having a structure having i) an optical fiber constituted of a first cover layer with which the surface of an optical-fiber bare fiber is covered, a second cover layer with which the first cover layer is covered and an optical-fiber bare fiber uncovered portion standing uncovered from the first cover layer and ii) an optical-fiber guide-in sleeve member (metallic sleeve) with which this optical fiber is fastened, where this optical-fiber guide-in sleeve member is constituted of a first columnar hollow portion into which an optical fiber with the second cover layer can be inserted, a second columnar hollow portion which communicates with the first one and into which an optical fiber with a first cover layer smaller in diameter than the first columnar hollow portion and a third columnar hollow portion which communicates with the second one and has a diameter larger than the second columnar hollow portion and in which the first cover layer and the optical-fiber bare fiber are held, where the air space between the optical fiber with the second cover layer and the first columnar hollow portion is filled with an adhesive to bond them, the air space between the first cover layer, the optical-fiber bare fiber and the third columnar hollow portion is filled with a solder, and a cover of an adhesive is provided at the leading end portion of the solder.
The metallic sleeve of this optical-fiber feedthrough is fastened to the package sidewall of the optical communication module by soldering or seam welding to effect hermetic sealing.
Now, in the optical-fiber feedthrough disclosed in Japanese Patent Application Laid-open No. H8-15572, the portion fastened with solder and the portion fastened with resin adjoin to each other inside the pipe (metallic sleeve). Hence, when the metallic sleeve of the optical-fiber feedthrough is soldered or seam-welded to the package sidewall of the optical communication module, the heat of the soldering or seam welding tends to be conducted to the resin-covered portion of the optical fiber and to the resin (adhesive) with which the optical fiber is fastened to the metallic sleeve, so that, at the worst, it has occurred that the stress to the optical fiber due to the deformation of the resin makes the optical-fiber bare fiber break.
In the optical-fiber feedthrough disclosed in Japanese Patent Application Laid-open No. H8-114723, too, the portion fastened with solder and the portion fastened with resin are adjacent to each other inside the optical-fiber guide-in sleeve member (metallic sleeve). Hence, like the optical-fiber feedthrough disclosed in Japanese Patent Application Laid-open No. H8-15572, there has been a problem that the optical-fiber bare fiber tends to break when the metallic sleeve of the optical-fiber feedthrough is soldered or seam-welded to the package sidewall of the optical communication module.
The present invention has been made taking note of such problems. Accordingly, an object of the present invention is to provide an optical-fiber feedthrough that can make the optical-fiber bare fiber not easily break when it is attached to the package sidewall of the optical communication module.
Another object of the present invention is to provide an optical-fiber feedthrough that enables sealing treatment by a simple method, making use of a solder having a higher melting point than any conventional one, and enables the optical communication module to be manufactured stably and to have highly reliable sealing structure.
Still another object of the present invention is to provide an optical-fiber feedthrough that can make the optical fiber not easily come out of the optical-fiber feedthrough when the optical fiber is pulled (i.e., has a high pull strength).